Repairing Punctures

tarquin_foxglove

I used to have a bike with 26in wheels and when I got a puncture I repaired it, usually successfully.

Since I've got a hybrid with 700c wheels running at 100-120 psi, its been impossible to repair punctures.

Is that because of the pressure or do I need to work on my technique?
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singlespeedexplosif

you need to work on your technique.

dangreen

Hi,

Can'tsay i've ever bothered trying to repair them. I just swap the inner tube out, really don't fancy the idea of the repair failing on me on the way home!

il_principe

+1

lost_in_thought

I swap the tube, take the punctured one home and have a good look at it then repair in good light and a warm, relaxed setting! Then I pump the repaired tube up a bit too far and see if my repair holds.

wgwarburton

Technique.

Anyone tried those new-fangled "self-adhesive" patches? Don't like the look of 'em meself... Surely they can't be trusted at 100psi+?

I carry a spare tube. Swap it in on the roadside then fix the tube with rubber-solution & feather-edge patches on the train.

My toolkit consists of: 15mm ring spanner cum tyre-lever, 1 x spoke wrench, 5mm allen key, patch kit and frame fit Zefal pump plus a couple of Zip-Ties.

Gets me out of most situations but I was stranded last week when the sidewall blew out of my rear tyre, leaving a four-inch split. Should have changed it sooner :-(

Cheers,
W.

the_hundredth_idiot

Buy new bike with 700C wheels (rather than 26 inch on current MTB). CHECK

Continue to carry around old 26 inch spare inner tube in case of punctures. CHECK

Doh! :oops:

Good reminder from this thread to pop out at lunchtime and get a new tube that'll actually fit the new bike.

singlespeedexplosif

Anyone tried those new-fangled "self-adhesive" patches? Don't like the look of 'em meself... Surely they can't be trusted at 100psi+?

yep - I use the Park ones - they're fine at 120psi

always_tyred

Its not the adhesive that's holding the air in at those pressures. Think about it - the valve hasn't got any adhesive but it holds air pretty well. So be cautious testing your repaired tubes outside of the tyres.

And kids, don't do drugs.

Thankyou very much.

tarquin_foxglove

singlespeedexplosif wrote:

Anyone tried those new-fangled "self-adhesive" patches? Don't like the look of 'em meself... Surely they can't be trusted at 100psi+?

yep - I use the Park ones - they're fine at 120psi

That's not technique, that's technology.

schlepcycling

Always Tyred wrote:

Its not the adhesive that's holding the air in at those pressures. Think about it - the valve hasn't got any adhesive but it holds air pretty well. So be cautious testing your repaired tubes outside of the tyres.

And kids, don't do drugs.

Thankyou very much.

Surely it's the adhesive that holds the patch over the puncture and it's the patch that creates the seal and stops the air from escaping, so if the adhesive doesn't hold the patch then the patch fails and the air escapes or am I missing your point?.

woodford2barbican

schlepcycling wrote:

Always Tyred wrote:

Its not the adhesive that's holding the air in at those pressures. Think about it - the valve hasn't got any adhesive but it holds air pretty well. So be cautious testing your repaired tubes outside of the tyres.

And kids, don't do drugs.

Thankyou very much.

Surely it's the adhesive that holds the patch over the puncture and it's the patch that creates the seal and stops the air from escaping, so if the adhesive doesn't hold the patch then the patch fails and the air escapes or am I missing your point?.

I think what Senor Schlepcycling is getting at is that the pressure of the tube & patch against the tyre also has something to do with it.

Personally I always patch - I like my inner tubes more the greater of patches they have.

It makes me feel like an old campainger reminiscing over scars gained and battles fought when patching a hole.

always_tyred

Actually I'm kind of trying this out for size.

I think that, if it were possible to position a patch over the hole in a tube and inflate the tube at a greater rate than the loss of air through the whole, it would eventually seal. The glue facilitates this progess by holding enough pressure to get to that point, and holding the patch in the right place to begin with. The hole is plugged by the seal between the tube and the patch (hence, patches are soft) as the tube is pressed out against it.

Actually, you'd probably find that its the glue that's doing this (as a consequence of its elastic properties rather than its adhesive properties) with the patches we use. But essentially, all I'm describing is the same way that a calve of a tubless tyre on a car seals.

Again, were it possible to inflate the tube to great enough pressures outside of the tyre without it becoming a life raft, you would find that the glue would fail at relatively low pressures and the patch would pop off. That contact cement doesn't chemically react with the tube surface, its pretty rudimentary stuff.

Damn, I'm almost tempted to go and paste loads of contact cement on the inside of my tyres and see if I can get the tubes to seal against them, now! Has anyone ever tried this as a means of overcoming a "damn, there's only foil and no patches in this little box" moment?

wgwarburton

I think you're wrong.

The glue is called called "rubber solution" because it dissolves the tube and patch, so that they are chemically welded together (I know it isn't technically rubber any more, but bear with me, OK?). If the patch isn't glued properly then air leaks out of the edges, in fact you can sometimes see a bulge in the patch where air has got between the tube and the patch because of poor adhesion, though the patch is holding at the edges.
It is weaker than an untouched tube but you'd be surprised how well a properly applied patch holds up to inflation- they don't just peel off if the glue's had time to cure properly.

A patch won't hold high pressure without the support of the tyre, any more than a tube will, but if your theory worked then a properly positioned patch would always hold, regardless of the efficacity of the glue, and I can tell you from bitter experience that that isn't the case.

Cheers,
W.

woodford2barbican

WGWarburton wrote:

...... where air has got between the tube and the patch because of poor adhesion, though the patch is holding at the edges....

This poor adhesion - is it the result of poor technique?

lost_in_thought

As someone who tests the patches by overinflating the tube, I can confirm that it is the adhesion rather than just the pressure of tube against tyre that seals the puncture.

I don't doubt that the tyre helps though!!

always_tyred

WGWarburton wrote:

I think you're wrong.

The glue is called called "rubber solution" because it dissolves the tube and patch, so that they are chemically welded together (I know it isn't technically rubber any more, but bear with me, OK?). If the patch isn't glued properly then air leaks out of the edges, in fact you can sometimes see a bulge in the patch where air has got between the tube and the patch because of poor adhesion, though the patch is holding at the edges.
It is weaker than an untouched tube but you'd be surprised how well a properly applied patch holds up to inflation- they don't just peel off if the glue's had time to cure properly.

A patch won't hold high pressure without the support of the tyre, any more than a tube will, but if your theory worked then a properly positioned patch would always hold, regardless of the efficacity of the glue, and I can tell you from bitter experience that that isn't the case.

Cheers,
W.

That's entirely possible.

However, the patches I use presently can be peeled right off and the glue appears to be similarly removeable. In addition, I don't see that there is sufficient free solvent present in the "glueless" patches to achieve what you say. I do not think that the glue on those patches undergoes any change whatsoever following application. They are simply elaborate post-its.

The hypothetical "out of tyre" experience is tricky - when you over inflate a tube out of the tyre and it becomes a hazard to shipping, there's still a pretty low pressure in it.

Rubber solution is not rubber, and its not clear to me if it cures or dries. It may or may not solvate the material of the tube and cure (or dry) "intimately" with the material of the tube. However, its present to provide a very tacky, fresh surface to meet the freshly exposed surface of the patch. Surfaces get dirty at the molecular level very quickly. When I mend a flat, I let the rubber solution dry and a physcial bond is formed with the patch. The idea of roughing up the tube is to increase its surface area because you can't get as good a physcial interaction (note physical, not chemical) to the dirty tube surface. Using a solvent which penetrates the tube is a good way of getting around this and would probably be advantageous. However, do you apply the patch when its wet or dry? I think the latter, in which case the puncture prevention is still basically the same mechanism as the Skinflint patches I use.

I'm sticking to my guns. More out of curiosity than any real conviction that I'm right.

always_tyred

lost_in_thought wrote:

As someone who tests the patches by overinflating the tube, I can confirm that it is the adhesion rather than just the pressure of tube against tyre that seals the puncture.

I don't doubt that the tyre helps though!!

Try putting 40 or 50 psi in. Wear safety glasses though.

I'm arguing (for the hell of it ) that the pressure during the out of tyre tests is negligible and that the result is (for the purposes of this arguement) null. I argue that the test merely correlates with the resultant in-tyre performance, as well as it be extremely satisfying to observe that the patch is holding.

Littigator

Always Tyred wrote:

WGWarburton wrote:

I think you're wrong.

The glue is called called "rubber solution" because it dissolves the tube and patch, so that they are chemically welded together (I know it isn't technically rubber any more, but bear with me, OK?). If the patch isn't glued properly then air leaks out of the edges, in fact you can sometimes see a bulge in the patch where air has got between the tube and the patch because of poor adhesion, though the patch is holding at the edges.
It is weaker than an untouched tube but you'd be surprised how well a properly applied patch holds up to inflation- they don't just peel off if the glue's had time to cure properly.

A patch won't hold high pressure without the support of the tyre, any more than a tube will, but if your theory worked then a properly positioned patch would always hold, regardless of the efficacity of the glue, and I can tell you from bitter experience that that isn't the case.

Cheers,
W.

That's entirely possible.

However, the patches I use presently can be peeled right off and the glue appears to be similarly removeable. In addition, I don't see that there is sufficient free solvent present in the "glueless" patches to achieve what you say. I do not think that the glue on those patches undergoes any change whatsoever following application. They are simply elaborate post-its.

The hypothetical "out of tyre" experience is tricky - when you over inflate a tube out of the tyre and it becomes a hazard to shipping, there's still a pretty low pressure in it.

Rubber solution is not rubber, and its not clear to me if it cures or dries. It may or may not solvate the material of the tube and cure (or dry) "intimately" with the material of the tube. However, its present to provide a very tacky, fresh surface to meet the freshly exposed surface of the patch. Surfaces get dirty at the molecular level very quickly. When I mend a flat, I let the rubber solution dry and a physcial bond is formed with the patch. The idea of roughing up the tube is to increase its surface area because you can't get as good a physcial interaction (note physical, not chemical) to the dirty tube surface. Using a solvent which penetrates the tube is a good way of getting around this and would probably be advantageous. However, do you apply the patch when its wet or dry? I think the latter, in which case the puncture prevention is still basically the same mechanism as the Skinflint patches I use.

I'm sticking to my guns. More out of curiosity than any real conviction that I'm right.

Oops, sorry I took a wrong turn and must have wandered into an Open University programme circa 1970s

snooooooooooore

always_tyred

I know they don't teach science in schools any more kids, but it really IS interesting.

I'll just go and drop some potassium into this beaker to demonstrate....

Max_Man

Had to fix a puncture this morning on the good bike, first one since I bought the bike and the first one on a thin wheeled road bike. Wow these tyres are hard to get off the rim. :shock:

Got it done and slipped out for a quick 25 to test it.

(I used standard rubber cement and a rubber patch, I have some of those quick self adhesive ones but I'll keep them for the side of the road)